1. Field of the Invention
The invention relates to a composite pipe with an integral socket applied by injection-molding.
2. Background Art
EP 0 108 598 B1 teaches to provide the portions of composite pipes which are to form a pipe socket with a smooth-walled external-pipe section and a smooth-walled internal-pipe section which are not united. For the production of a socket, the internal-pipe section is cut out subsequently. This socket is not dimensionally stable. This method is complicated and has not been successful in practice.
It is known from U.S. Pat. No. 5,320,797, in the area where a socket is to be formed, to combine the two streams of plastic melt which constitute the external tube and the internal tube, a socket thus being produced in-line. By simultaneous reduction of the advance speed of the mold that serves for the manufacture of the composite pipe, more plastic material per unit length of the pipe is supplied to the portion of the socket so that the socket exhibits a higher vertex resistance to pressure than in case the amount per unit length of plastic material had not been increased.
A similar method is known from the more recent WO95/01251.
U.S. Pat. No. 4,779,651 teaches a composite pipe having a socket molded on in-line, in which annular elevations elastically deformable radially inwards are formed on the corrugations crests for the purpose of compensation of tolerances. In the vicinity of its insertion section, the socket is provided with an outer crimp which reinforces the annular rigidity.
It is known from EP 0 595 742 B1 to assemble composite pipes by means of a kind of a slide lock. In this case, one pipe section at a time is provided with a socket which is likewise a composite pipe.
EP 0 385 465 A2 teaches subsequently to provide a composite pipe with a socket by one end being expanded. The corrugation crests of the external pipe are flattened.
A basic problem of all the sockets injection-molded on composite pipes resides in that the socket are not always sufficiently dimensionally stable. This is due to the fact that composite pipes obtain their rigidity from the special box-type profile of the composite pipe and not from the thickness of the wall material. The known integral sockets lack this structure. Minor improvement is attained by the mentioned reinforcing crimps in the vicinity of the insertion section of a socket. Moreover, composite pipes having the known sockets of greater nominal widths cannot be produced without any problems, because cooling problems will occur. Since, conditioned by construction, the wall thicknesses of the external pipe as well as of the smooth internal pipe will increase when the nominal width of the composite pipes increases, discharge of the energy stored in the plastic melt will no longer take place during in-line injection-molding of a socket neither outwards via the shells nor inwards via the cooled caliber. The reason why this concerns the sockets resides in that, in the vicinity of the socket to be produced, the internal tube is no longer in contact with the caliber, which results in that either the manufacturing rate must be reduced strictly with the nominal widths of the composite pipes to be manufactured growing, or that the socket molded on in-line is not formed accurately and does not conform to tolerances. These drawbacks cannot be tolerated in particular in the case of drain and/or storm water pipes, on which high demands are put, regarding the leak-proofness of a socket connection.